Influence of pH on the Properties of Lactobacillus helveticus Aminopeptidase

We examined the influence of pH on the physical and biochemical characteristics of partially purified aminopeptidase from Lactobacillus helveticus ATCC IS009. Optimum activity was obtained at 4SOC between pH 6.5 and 7.0. o-Phenanthroline was the best inhibitor over the entire pH range studied; however, several inhibitors, including EDTA, iron, sodium chloride, and phosphate glass, were more inhibitory at low pH. As pH was reduced, thermal stability of the enzyme and resistance to freezing and thawing increased, but substrate affinity decreased. Results suggest that peptidase stability may be an important factor in cheese ripening.